Effective cost estimation is the most challenging activity in software development. Software cost estimation is not an exact science. Cost estimation process involves a series of systematic steps that provide estimate with acceptable risk. Some prevalent LOC based models are- Bailey Basili model, Alaa F. Sheta G.E. Model, and Alaa F. Sheta, Model 2 [1] .Two new models, based on fuzzy logic sizing, are presented in this paper. Rather than using a single number, the software size is regarded as a triangular fuzzy number. We can optimize the estimated effort for any application by varying arbitrary constants for these models. The developed models are tested on 10 NASA software projects [2], on the basis of four criterions for assessment of software cost estimation models. Comparison of all the models, cited above, is done and it is found that the developed models provide better estimation. Key Words: LOC based models. NASA Software Projects, Fuzzy logic, Triangular Fuzzy Number, Membersh...